1. Field of the Invention
The present invention relates to a control unit for controlling the drive of loads, such as a light source and a heat source, in an image forming apparatus, such as copying machine or facsimile.
2. Description of the Prior Art
A copying machine for copying an original image has loads activated by energization, such as a halogen lamp for illuminating an original document and a fixing heater for firing a copied image.
The halogen lamp must illuminate at a predetermined light intensity in order to attain a desired image density. Accordingly, the energization of the halogen lamp is controlled by a control circuit called a lamp regulator to maintain a constant level of light intensity. However, a lamp regulator cannot sufficiently compensate for a large or abrupt change in a power supply voltage.
A lamp regulator usually detects a mean value of the power supply voltage and controls the energization based on the mean value. However, since the light intensity of the halogen lamp is related to an effective value of the power supply voltage (applied voltage), such a light intensity control attains only approximate control.
In order to eliminate such an error, a lamp regulator has been proposed, in which a circuit configuration is improved such that the light intensity control by the detected mean value approaches the effective value. However, the circuit configuration is complex and cost increases.
It has also been proposed to control the energization of the load by digital operation using a microcomputer. However, the processing capability of the microcomputer may not be large enough to satisfy the requirement of precisely controlling a wide control range of an object, or a large portion of a memory of the microcomputer may be used for the control and other controls are not sufficiently attained.